Fish pumps are used in the fishing industry to transfer fish from a fishing vessel to a fish processing plant, for example: Fish pumps found in the prior art are not usually designed to prevent shock and stress to the fish being moved. As may be appreciated from the following examples of fish pumps found in the prior art, fish being transported by conventional fish pumping systems are submitted to large gradients of push and pull forces, and shocks from funnelling passages and other piping constrictions.
A first example of a fish pumping system found in the prior art includes    U.S. Pat. No. 2,736,121 issued to H. J. Kimmerle on Feb. 28, 1956. In this type of pumping installation, the fish are drawn from a fishnet by vacuum pressure and fed through a rotary valve and into the hold of a boat. The rotary valve is required for maintaining the system under vacuum pressure.
Other types of vacuum-type fish pumps are described in:    U.S. Pat. No. 3,583,365 issued to D. G. Harden on Jun. 8, 1971;    U.S. Pat. No. 3,871,332 issued to T. Hayashi on Mar. 18, 1975;    U.S. Pat. No. 4,293,250 issued to T. Hayashi on Oct. 6, 1981;    U.S. Pat. No. 4,770,610 issued to R. A. Breckner on Sep. 13, 1988;    U.S. Pat. No. 4,826,362 issued to T. Hayashi on May 2, 1989;    U.S. Pat. No. 5,002,463 issued to R. A. Breckner et al., on Mar. 26, 1991;    U.S. Pat. No. 5,078,579 issued to R. M. Ryan on Jan. 7, 1992;    U.S. Pat. No. 6,161,504 issued to W. W. Jungling et al., on Dec. 19, 2000;The fish pumps included in this latter group of patents all have a large tank where a vacuum pressure is created. Fish and upload water from a first location are drawn through a one-way valve and into the large tank. When the tank is full, the pressure inside the tank is changed from a vacuum pressure to a positive pressure to force the fish and water out of the tank, through a second one-way valve and toward a second location.
In a third group of fish pumps from the prior art, the following publications were found:    U.S. Pat. No. 4,558,990 issued to S. W. Roach on Dec. 17, 1985;    U.S. Pat. No. 4,702,676 issued to A. P. Westfall et al. on Oct. 27, 1987;    U.S. Pat. No. 4,756,671 issued to E. L. Grimes on Jul. 12, 1988;    U.S. Pat. No. 7,462,016 issued to P. B. Lindgren on Dec. 9, 2008;These installations are related to jet pumps where a stream of air or water is fed into the nozzle of a large hose. This stream of air or water induces a negative pressure in the nozzle thereby drawing upload water and fish through the nozzle of the hose and into the hose.
In yet another type of fish pump found in the prior art, the following documents describe pumps with special impellers to minimize damage to the fish.    U.S. Pat. No. 4,193,737 issued to G. H. Lemmon on Mar. 18, 1980;    U.S. Pat. No. 4,768,920 issued to M. I. Gurth on Sep. 6, 1988.In the first-mentioned pump, the impeller has large helical-spiral passages allowing fish and water to pass through the pump without being caught by the impeller. In the second-mentioned pump, the impeller is a disc-type blade-less impeller so that fish and upload water are drawn through the pump and moved by friction force only without shock to the fish.
Although the fish pumps of the prior art deserve undeniable merits, there is still a need in the fish processing industry for a gentle pumping system that is particularly suitable for handling large quantities of relatively big fish without bruising the fish. More particularly, there is a need in the fish processing industry for a fish pumping system capable of gently handling 4,000 to 6,000 farmed salmon per hour, wherein each fish can weigh up to 12 kg.